Electricity demand continued to grow as the temperature increased yesterday; at 3.30pm, Energex said usage as extreme, with 4310 megawatts being drawn, down from 4520 megawatts earlier in the day, and short of the 4636 megawatt record set in February in 2010.

Brisbane last experienced a December top of 39 degrees was Boxing Day 2001.

But the hottest December day on record came on December 7, 1981, when the mercury topped 41.2 degrees.

The Queensland Fire and Rescue Service has mustered additional resources across the state's south-east with extreme fire warnings current.

A strike team from Toowoomba arrived in Roma on Sunday and incident control points have been established in Warwick, Dalby and Roma.

Six water bombers and two aerial support aircraft are also positioned across various parts of south western Queensland.

Queensland Health has urged residents to drink plenty of fluids and remain in air-conditioning where possible to avoid suffering heat stroke or exhaustion.

Residents are also asked to check on elderly neighbours, or friends and family, who may be more vulnerable in the hot weather.

Heat exhaustion usually develops over a couple of days. Symptoms may include muscle cramps, heavy sweating, paleness, dizziness, nausea or vomiting and fainting.

People suffering heat stroke require urgent medical attention.

Tips to prevent heat-related illnesses:

Drink plenty of fluids - cool water is best. Don't wait until you are thirsty to drink, but drink regularly throughout the day. Urine colour is a good guide to hydration - it should be clear to light straw-coloured, not dark or gold.

Stay indoors in very hot weather, preferably in an air-conditioned building or ensure there is good air flow with fans and open windows.

Public venues, such as air-conditioned shopping centres and pools, can provide refuge from the heat.

People can also stay cool by taking cool showers or baths; soaking their feet in a basin of water; or wetting a bandanna or washer and wrapping it around their neck.